True inner peace is not something you can conceptualize with your mind. Is not actually a mind process at all. To access and experience true inner peace you need to be able to drop out of thinking about anything. This is usually the part of the process where people get stuck.
Very simply put, people don't feel they can trust anything that they can't wrap their minds around. Unfortunately this includes inner peace. If there is a topic or an issue that someone feels they don't understand, they no longer feel in control of the situation. When they don't feel in control of the situation they don't feel safe.
When this happens there are usually two major issues involved. The first is that there's some sort of buildup of trauma that perpetually causes them not to feel safe outside of controlling the situation. This is probably the most common. In this case, it is possible to release the traumatic energetic blockages lying in a persons system using the technique of meditation. That is another article for another time.
The other possibility is that they are caught up and narcissistic programming that will fundamentally stop them from doing anything they don't feel they're in control of. These cases are a little more rare.